SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 95 



insects and signifies liomologous parts through the entire class. For 

 the proximal division of the labium he suggests the term postmentum. 

 This division includes the fused cardines of the second maxillae and 

 the part of the labial sternum which is generally accepted as being 

 united with the cardines. The distal division of the labium, that part 

 which always carries the palpi and ligular lobes when these parts are 

 present, is now rather generally known as the prementum. It unques- 

 tionably represents the stipites of the second maxillae. 



The main divisions of the labium may remain as single parts, or 

 each may be subdivided into two or more sclerites. Snodgrass (1931, 

 pp. 483-484) states in regard to the postmentum that its " sclerotiza- 

 tion may take the form of one, two, or even three distinct plates." 



The terminology of the labium of insects in general seems some- 

 what more complicated than the morphology. Perhaps more atten- 

 tion has been given the sclerites than they deserve, considering their 

 secondary significance. The origin of the term mentum and its con- 

 nection with a definite region of the labium is rather obscure, but 

 inasmuch as it means " chin ", it was doubtless intended to apply to 

 that part of the fused second maxillae which supports the " lip." 

 Since the word labium has a common derivation with " lip ", it would 

 seem better, perhaps, to refer to the distal region of the second 

 maxillae, that part which is movable by muscles, as the labium. 

 Crampton (1921) has apparently the same idea when he calls the 

 distalmost division of the underlip region the " eulabium." 



In order to assist in understanding and correlating the systems of 

 terminology for the parts of the labium, the following table has been 

 compiled. It shows the names that have been applied to the same 

 divisions by the indicated workers. 



The complete musculature of the labium (salivary pump muscles 

 omitted) based on the condition as found in some of the more gen- 

 eralized forms (roach, pi. i, B; cricket, Snodgrass, 1931, fig. 24) is 

 shown in the diagrammatic representation (pi. i. A). It shows the 



